magnetic system of the soviet speaker 20gds-3. disassembled mid-range speaker

audio equipment magnetic system soviet dynamics 20gds3 disassembled speaker midrange core coil basket foam rubber glue suspension diffuser repair 20gds 15gd11 cap magnet ferrite vintage frequency revision upgrade professional tweeter monitor 35as electronic device music sixties loudspeaker grids brown studio brick wall dj electroacoustic technology subwoofer radio engineering black decoration diffusor sound